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Flu Shot: Influenza Vaccine and Side Effects

Thinking about getting a flu shot or influenza vaccine this year? The influenza vaccine is the best way to prevent the flu, and flu prevention should be a goal for everyone.

According to the CDC, up to 20% of Americans get the flu each year. More than 200,000 people in the U.S. are hospitalized each year, and somewhere between 3,000 and 49,000 deaths are flu-related. These statistics would decrease if more people took advantage of the opportunity to prevent flu with an influenza vaccine or flu shot.

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When should I get a flu shot?

Because the peak flu season may begin as early as October and run through May, the best time to get a flu shot is in September or October. It takes about two weeks for the flu shot to be most effective. You can still get an influenza vaccine in December or later -- flu season lasts well into spring -- but the earlier in flu season you get it, the better your odds of staying flu free.

What types of flu shots or influenza vaccines are available?

There are several types of flu vaccine:

  • The traditional flu shot. Injected into the muscle, it contains flu-virus particles that stimulate anti-flu immunity but can't cause the flu.
  • Egg-free flu shot. Unlike traditional flu vaccines, this one is not grown inside eggs. Doctors say all but those with the most severe allergic reactions to eggs can get a traditional shot with few side effects.   
  • The high-dose flu shot. Approved for people age 65 and older, the ingredients are the same as the regular flu shot, but the dose is higher, as the aging immune system needs more stimulus to produce adequate immunity.
  • An intradermal flu shot. Approved for people ages 18 to 64, the shot uses a tiny needle that only goes skin deep. It contains the same flu-virus particles as the traditional flu shot.
  • Nasal spray flu vaccine. Approved for some people ages 2 to 49, this vaccine, called LAIV for live attenuated influenza vaccine, contains a live, weakened flu virus. Clinical trials show that it cannot cause the flu. For in-depth information on this vaccine, see WebMD's What is FluMist?

Flu vaccines now come in two forms: trivalent vaccines protect against three flu strains (two Influenza A viruses and one Influenza B virus), while quadrivalent vaccines protect against four flu strains (two Influenza A and two Influenza B viruses). The traditional flu shot is available in both trivalent and quadrivalent forms, the high-dose flu shot and the intradermal flu shot only in the trivalent form, and the nasal spray flu vaccine only in the quadrivalent form.




How does the flu shot or influenza vaccine work to prevent flu?

Flu shots and the nasal flu vaccine work by causing antibodies to develop in your body. These antibodies provide protection against infection from the flu virus. This antibody reaction may cause fatigue and muscle aches in some people.

WebMD Medical Reference

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